SCOOT MC3

SCOOT MC3 (Managing Congestion, Communications and Control) enhances how SCOOT operates in
four key areas: communications, congestion control, bus priority and puffin pedestrian
facilities. In addition to the facilities available in previous versions, SCOOT MC3 has the
following new developments:

Time stamping of data

Communication systems are continually developing and analogue dedicated lines, which
currently most SCOOT systems depend on, are likely to become increasingly expensive and
ultimately not supported at all. A major new development has enabled SCOOT to make flexible
use of new communication systems and remove the reliance on second-by-second
communication. This increases the range of communication options available and
in particular allows the use of some of the newer data communications systems
e.g. ADSL, GPRS, G3 etc which are packet based. SCOOT has been modified to use
time-stamped data to allow for inconsistencies and delays in data packet
delivery. To accompany the time stamping development, the resolution at which
SCOOT stores some of the flow data has been reduced from 4 seconds to 1 second.
The effect of this change is to counter the possible reduction in timeliness
that the loss of second-by-second communication will introduce. It is predicted
that as long as any delays are of the order of only a few seconds the move away
from guaranteed second-by-second communication will have a negligible
operational effect.

Congestion supervisor

From the outset
the optimisers in SCOOT have acted to help to control congestion. Over the
years a number of additional facilities have been provided. These congestion
management features have been enhanced in SCOOT MC3 by the addition of a
congestion supervisor. The supervisor runs continuously in the background
searching for and analysing congestion problems. It will report its results
and help the engineer to make optimal use of all the facilities that are
available in SCOOT to manage congestion.

The congestion supervisor has been developed based on the information already
available within the SCOOT system. The aim of the supervisor is to continuously
monitor congestion throughout the SCOOT controlled network, to identify links
causing serious problems and to diagnose the probable reason for congestion
emanating from those links. The congestion problem and the recommended action
to take will then be reported to the users either directly from SCOOT or through
a supervisory system. Overall the aim of the congestion supervisor is to
target regularly recurring congestion rather than congestion caused through
incidents.

Identify nodes that are the cause of the congestion problem

Calculate congestion offsets on 'short' links

Identify possible changes to congestion importance factor

Diagnose problems when there are faulty links

Report/diagnose problems where the degree of saturation is low

Diagnose and report where a junction is overloaded

Stage skipping for bus priority

Enhanced bus priority in the form of stage skipping is now included in SCOOT
MC3. If a bus arrives at such a time in the signal cycle that it would have to
wait for a side road to be serviced, the existing bus priority would curtail
the length of that side road. With stage skipping the side road can be
completely omitted during this cycle, reducing delays to the bus waiting at the
signals. Comprehensive guidance is included within the system on when stage
skipping is appropriate and when it may be inadvisable - for instance, skipping
pedestrian stages is not recommended and the system provides complete
flexibility to configure the most appropriate solution for each situation.

Extensive tests in London during the development programme showed typical
average benefits of 4 seconds per bus through each junction with stage skipping.
As with all SCOOT bus priority features, stage skipping has flexible input
requirements. The approach of a bus can be indicated by on-vehicle
transponders activating special detectors, or the location can be provided by a
bus management system using any automatic vehicle location system.

Puffin pedestrian facilities (Modelling of Variable intergreen)

Puffin (Pedestrian User Friendly Intelligent) crossings are intended to become the UK standard for
signal controlled pedestrian facilities at stand-alone crossings and junctions.
Unlike pelicans, there is no flashing amber period, instead the length of the
red to vehicles is variable depending on the time that pedestrians take to
cross the road. In SCOOT MC3 the kernel has been modified to model the variable
intergreen period that follows the pedestrian invitation to cross stage rather
than assuming it runs for a fixed length. SCOOT MC3 accurately models the
on-street behaviour of Puffins and Puffin pedestrian facilities and thus
provides improved control and reductions in delay to vehicles.